The present invention pertains in general to the art of portable power tools; it relates, more particularly, to electric hand tools similar in nature to the well known and widely used electric drills.
The power head of a conventional portable electric hand drill includes a driven shaft carrying a chuck adapted to receive and hold any of a variety of cutters or the like. Drill bits are the most widely used cutters, but the chuck may be used to receive and grip the shanks of such different operative elements as, for example, routing cutters, burrs, screw driving implements, sanding discs, or polishing pads. All such elements are here lumped within the generic term "cutters or the like".
The common electric drill usually is made with a pistol grip handle, or something akin to it, and a switch trigger--so that the drill and its cutter are held and manipulated by one hand of the user. In some instances, a second handle is employed for two-handed manipulation. In either case, the human operator is left to his visual, muscular, and estimating skills for a determination of the angle at which a cutter such as a drill bit penetrates a workpiece and thus the angle of a drilled hole, for a determination of the depth of a blind hole, or for the path through which a routing or burring cutter is moved. The angles and depths of drilled holes are hard to control, and sufficient accuracy in routing a straight groove is almost beyond the skill of hand control by a human operator.
Because of these and other considerations, a whole host of accessories have been proposed for use with electric hand drills. Generally, these comprise some carriage into which the drill body is strapped or clamped, the carriage then being moved with mechanical action and guidance on a base so as to determine the angle of attack, the depth, or the path of the cutting element. Probably the most familiar of such accessories is a "drill press" accessory having a stand or base, and a carriage in which the electric drill is strapped together with a rack and pinion arrangement for moving the carriage vertically up and down.
Accessories of that type enable a power head or an electric drill to be employed with greater accuracy than, or for functions not achievable with, ordinary hand manipulation. But such accessories are in the main heavy, bulky and not portable; they convert an electric drill into a shop machine which usually serves only one purpose and which cannot readily be taken by a user to his attic or a country fishing cabin where different "on-site" jobs may need to be performed.